The organizers of Sunday's climate change rally on the National Mall are giving President Obama no room to maneuver when it comes to his upcoming decision on whether to allow TransCanada Corp.'s proposed Keystone XL pipeline to go forward. They say opposition to the oil pipeline has become a massive grass-roots movement composed of many of the same people who spent last year working to re-elect Obama, and who will accept no decision from their president that does not kill the pipeline.